We all know we should beware of false gods, but now we are being warned to beware of false heads, specifically Celtic heads that are not what they appear to be.
The warning has come from a historian, Ms Cathy Swift, who recently purchased two Celtic stone heads at a country house auction.
Celtic stone heads are a rare group of artefacts which date from the Iron Age and occur in clusters.
They have been found in the Raphoe area of Donegal, the Erne region of Fermanagh, around Armagh city and around Piltown, Co Kilkenny.
"Imagine my surprise, therefore, when during a country house auction I came across two remarkably Celtic-looking heads listed among a variety of stone objects in a job lot," she writes in the current edition of Archaeology Ireland.
"The heads were of Leinster granite and had the thick lips and long rectangular nose well known from objects such as the Boa Island figure and also apparent on a variety of Celtic heads from as far afield as Bohemia.
"One was similar in style to the so-called Sailor's Head, the other had eyebrows similar to a stone from Donegal now on display in Gartan Heritage Centre, Co Donegal, and a pointy chin similar to that found on the Maponus stone from the north of England."
The guide price was between £40 and £60. "Apparently there is more than one Leinster entrepreneur involved in the production of these heads, which are subsequently covered with yoghurt and buried to get the greenish antique tinge," the article stated.
Ms Swift said she was told later by a horticulturist, Ms Maria Penderville, that this was a well-known technique much vaunted in gardening books and magazines.
The application of cow dung has similar effects.
Ms Swift, who works at the History Department in University College Dublin, reminded readers that the National Monuments (Amendment) Act, 1994, states that no person can buy, sell or acquire an archaeological object without reporting it to the Director of the National Museum within 30 days.